1. Field of the Invention
The present invention provides an improved process for making aryl esters from aromatic hydrocarbons such as benzene, naphthalene, anthracene, biphenyl, phenanthrene, fluorene, terphenyls, and the like, which comprises the reaction of a mixture of an aromatic hydrocarbon, molecular oxygen, a carboxylic acid, and optionally a hydrocarbon solvent, in the liquid phase in the presence of a catalyst which is composed of palladium or a compound of palladium, a compound of chromium and a compound of at least one metal selected from the group consisting of Zn, Mn, Sn, Co, and Ni.
2. Description of the Prior Art
The manufacture of phenol by the direct oxidation of benzene with oxygen is known. There are, for instance, thermal processes which are performed at very high temperatures in which the phenol formed is susceptible to further oxidation so that considerable loss of yield occurs as is disclosed in U.S. Pat. No. 2,223,383. In the presence of catalysts, the oxidation can be carried out at somewhat lower temperatures as in U.S. Pat. No. 3,133,122 but the reactions have been plagued by low conversions and excessive production of unwanted by-products as is disclosed in U.S. Pat. No. 2,392,875.
It has been proposed to make phenyl acetate and biphenyl from benzene and acetic acid in the liquid phase in the presence of palladium acetate and without added molecular oxygen by a stoichiometric reaction in Chem. and Ind., Mar. 12, 1966, page 457.
U.S. Pat. No. 3,542,852 discloses the preparation of hydroxy aromatic compounds by reaction of an aromatic compound and oxygen in the presence of a catalyst composed of iron, a noble metal or a compound of either in the presence of a nitrate ion and a carboxylic acid. More recently the preparation of phenyl esters and phenols by the reaction of benzene, molecular oxygen and a lower aliphatic carboxylic acid in the presence of a catalyst composed of a Group VIII metal (U.S. Pat. No. 3,642,873) or a compound of such metal (U.S. Pat. No. 3,651,127) have been disclosed. Similarly variations in this type of reaction have been disclosed in U.S. Pat. Nos. 3,646,111; 3,651,101; 3,772,383; 3,959,352 and 3,959,354. U.S. Pat. No. 3,959,354 concludes that liquid phase reactions of this type, because of problems of catalyst elution, etc., are disadvantageous for an industrial process. U.S. Pat. No. 3,772,383 describes a liquid phase reaction using a very complex catalyst system which includes the use of nitric acid and a lower aliphatic carboxylic acid such as acetic, propionic, butyric, etc. U.S. Pat. No. 3,644,486 describes the catalytic manufacture of oxacylation products and optionally hydroxylation products of condensed aromatic compounds, saturated aliphatic or cycloaliphatic carboxylic acids and molecular oxygen in the presence of a noble metal of Sub-Group VIII of the Mendeleef Periodic Table or compounds thereof. This Patent also discloses that transition metals can be used with the Group VIII metals and that carbonates or acylates of alkali or alkaline earth metals may also be used as activators in the catalyst system. Although extremely low yields of hydroxylation product are shown.
Generally speaking, these prior art processes deal for the most part with vapor phase oxidation reactions, or liquid phase reactions in which all of the reactants (except oxygen in some instances) are initially included in the reaction mixture and they use lower alkyl carboxylic acids such as acetic acid and propionic acid. Moreover, in general the prior art catalytic processes have produced low conversions, usually less than 10%, with poor selectivity to the desired aryl ester, and the hydroxy aromatic compound, such as phenol or naphthol, is often a primary product. The use of the lower saturated carboxylic acids, primarily acetic acid, in the catalytic oxidation process produces a highly corrosive system which can cause reaction equipment corrosion problems and excessive recyle costs as well as the extremely poor conversions and selectivities mentioned above. None of the prior art methods disclose the continuous addition of the aromatic hydrocarbon, the continuous removal of water from the reaction mixture as it forms, nor do they disclose or suggest the use of a solvent or the applicants' catalyst for the higher aromatic compounds in Applicants' process.